Re:
2) I followed that thread with interest, I like the theory of stripping BS tags e.g. I don't want those picard tags and I have seen other stray tags before that MB would have removed in the current set up. Conversely, I would not like tags that I don't know about being stripped without my knowledge during this processing. This is a tricky feature. perhaps a tag exception/inclusion list? I dunno, hmm.
I can understand why someone would want to get rid of extraneous tags. That's part of what I do when I process them in Picard.
The trouble is that there's no way to avoid this "feature" in MB, and there's no reason for the user to think that format converter affects anything except the format. Likewise, the file replace feature claims to preserve the tags on the replaced file exactly, but it does not.
Sorry, I don't think you need convincing, I'm just griping,

I would think having a separate "tag cleaner" or something would be the ideal solution. That way people could remove extra tags even if they weren't converting or replacing a file.